Active Region UV Atlas

The spectrograms used for the Atlas are from the second HRTS rocket flight, known as HRTS II, flown on 13 February 1978 aboard a Black Brant VC rocket (NASA Flight 21.042) at White Sands, New Mexico. During the rocket flight the slit was oriented radially from the solar disc center through the active region McMath 15139, including a sunspot, and across the solar limb. The Solar Pointing Aerobee Rocket Control System (SPARCS) kept the spectrograph slit positioned on the solar surface during the observing time of 4.2 minutes.

The spatial resolution on this flight was 2 arcsec with a time resolution from 0.2 - 20.2 sec. The HRTS spectra were recorded on Eastman Kodak 101-01 photographic film. Microphotometry of the spectrograms has been carried out at the Institute of Theoretical Astrophysics in Oslo.

The data reduction includes correcting the spectral images for geometrical distortion, Fourier filtering to remove high frequency noise, transformation to absolute calibrated solar intensity and calibration of the wavelength scale. The absolute intensity calibration was obtained by comparing relative intensity scans of a quiet solar region with absolute intensities from the Skylab S082B calibration rocket, CALROC The resulting absolute intensities are accurate to within 30% (rms).

The wavelength scale was established using solar lines from neutral and singly ionized atoms as reference lines. From this wavelength scale velocities accurate to 2 km/s can be measured over the entire wavelength range. The measured velocities are, however, relative to the average velocity in the chromosphere where the reference lines are formed.

The Atlas contains spectra of three different areas in the sunspot and also of an active region and a quiet region. The selected areas are averaged over several arcsec, ranging from 3.5 arcsec in the sunspot to 18 arcsec in the quiet region. The transition region lines in the Atlas show the most extreme example known of downflowing gas above a sunspot, a phenomenon which seems to be commonly occurring in sunspots.

One of the selected areas in the sunspot is a light bridge crossing the spot. This is the most interesting sunspot region where the continuum radiation is enhanced and measurable throughout the HRTS spectral range. A number of lines appear which do not occur in the regular sunspot spectrum.

The Atlas is available in a machine readable form together with an IDL program to interactively measure linewidths, total intensities and solar wavelengths. See: zeus.nascom.nasa.gov/~pbrekke/HRTS/